The present invention relates to a watchcase, and more specifically to means for fixing a watch crystal to the top of the body of a watchcase.
There are many known devices for tightly and removably fixing a flat crystal to the top of the body, said crystal extending, at least over a portion of its periphery, to the very edge of the body on which its lower face rests.
For example, Swiss Pat. No. 592,911 describes a sealed watchcase of a rectangular shape in which the crystal is held by two parallel tracks formed at opposite sides of the case. These tracks form dihedral angles, the top surface of which bears against the bevel edge of the crystal. During assembly, a sealing strip positioned by hand is dropped into the top opening of the body, and the crystal is then slipped laterally into the tracks. As the crystal is laterally engaged, the sealing strip is gradually compressed. Thereafter it exerts an axial pressure on the crystal, pressing it firmly against the upper track surface.
This arrangement, however, has several disadvantages including the risk of damaging or displacing the seal while the crystal is being slipped over it by bearing down on it to engage the crystal in the tracks. This difficulty has been resolved in another type of watchcase described in applicant's European Patent Application 0,006,077, (U.S. Pat. No. 4,198,811) where the crystal is retained on two opposite sides in projecting portions of the case between which it is engaged from above, thus compressing a sealing strip. Then the crystal is secured by cylindrical pins inserted laterally in matching holes made half in the case and half in the bevel of the crystal.
A common feature of these various solutions is that the edge of the crystal is involved in its attachment to the body, and this obviously limits the possibility of these solutions with very thin crystals, for example between 0.5 and 0.8 mm in thickness. In these various embodiments, it is necessary at the time of assembly, in order to compress the seal to subject the crystal to an axial pressure at least as great as that by which it is desired that the seal shall afterwards bear against the crystal. This presents a serious risk of breaking a very thin crystal when inserting it if this pressure is too great or of obtaining an imperfect seal otherwise.
Lastly, in these known solutions, the sealing strip in the assembled state of the case is always slanted radially inward with respect to the surface of contact between the crystal and the fixation members. This slant presents no problem with comparatively thick and rigid crystals, but the bending stress it generates may subject very thin crystals to a strain at the surfaces of contact resulting in a poor seal where the edges of the crystal are not provided with fixation members.
An object of the invention, then, is to propose a novel watchcase design of the above-mentioned type, in which the crystal may be engaged laterally in fixation members providing grooves, but in which it is not necessary to subject it to axial pressure at the time of assembly, and in which the crystal is held not by its edge but by its upper face. This construction is especially well suited to the fixing of very thin crystals and to protecting their vulnerable areas, such as their corners in the case of crystals of polygonal shape, against physical shock.